So what’s the big deal? Why not just leave them where they are and let them get snowed on? The roots of a plant in a container aren’t insulated from the cold as well as roots growing into the soil. A general rule of thumb is that a plant in a container needs to be two USDA hardiness zones hardier than the plants in the ground. So if the plants you have in containers are only as hardy as needed for your climate, they are not going to survive the winter unprotected. I am not talking about annuals–which we expect to die before winter–or tropical plants, such as dahlias and cannas–which must be dug and stored frost-free in order to survive–but perennials, small shrubs, and tree seedlings, which would do just fine had they been planted in the garden in a timely manner.
Store in a Sheltered Location
The easiest way to solve this problem is to put those potted plants in a location that is two hardiness zones warmer than usual for you. An insulated garage or garden shed would suit the purpose.My detached garage is not insulated, but that’s where I’m storing three berry plants in large ornamental containers. Neither of the other methods will suit, in this case, so I’m crossing my fingers and hoping for the best. If they survive, you will hear all about it next spring. Margaret Roach is the only gardener I know who insulated her garage/shed expressly to winter over some plants in pots.
Store in a Spare Bit of Earth
If you don’t have many container plants to protect, you could tuck them into some unused ground where a temporary hole would not be a problem. That way, their root balls would be protected by the surrounding earth without being disturbed by transplanting, when they are only going to be moved again come spring. Some people use a corner of their vegetable garden for this. I had a bunch of rooted shrub cuttings from a propagation workshop I had attended, and a big bare spot where an enormous barberry had been pulled out.
Bury Them With Leaves
But what if you have a lot of plants in pots? Like, say, forty-five?For the last two years, I have placed a bunch of plants in containers in a sheltered corner and covered them with leaves. They have come through with only minor losses so I feel somewhat confident about sharing this method with you. (We haven’t had especially severe winters the last two years, which is why I am not wholeheartedly confident.) Faced with a large inventory that you wish to protect, you may not have any choice but to use this method. Try to find a corner of the house that faces north. Using a corner of the house provides some heat. A north-facing location will stay out of winter’s occasional sunshine and not be as subject to thawing, which can bring a plant out of dormancy, making it more vulnerable to cold damage. Most of these plants had temporary wooden labels, because at the time I was certain that–unlike previous years–they would all be planted well before November. So before I stacked the pots, I relabeled them all with plastic labels. Mold grows on wooden labels, rendering them illegible after a time. For good measure, I wrote down each plant as I labeled it. (That’s why I know there’s forty-five pots stacked up there.) That way, this winter I can actually figure out where I’m going to plant them all in the spring.
With the help of my 11-year-old offspring, I loaded leaves into my garden cart and took them to the back of the house. A lilac bush prevented us from getting all the way into this area and just dumping the leaves. So we stuffed them into tub-trugs and then poured them over the stack of potted plants. I made sure leaves got stuffed behind and in between the pots. We had to get three or four garden carts full to make sure they were all covered.As you can see, this is not up against the house, but up against the lattice that skirts the deck and stairs. But I suspect it still gets some warmth from the house.
Questions You May Have
Don’t the leaves blow away?
It helps to set this up in a protected corner, but I do check on it every so often before we get our permanent snowpack. Once there is an accumulation of snow, the leaves don’t go anywhere. Even if the snow melts, it has usually packed down the leaves and the frozen moisture that has crept in kind of glues them together.
When do you uncover them in spring?
When I see perennials in the garden start to show new growth, I start to gradually remove the leaves from the pile, removing more each day. Sometimes I see etiolated growth snaking out from the leaves, and then I really know it’s time to uncover them.
Do you have problems with rodent damage?
Chipmunks and voles are prevalent in this area anyway, and I have found evidence of tunnels both in a few pots and in the ground at the bottom. But since most of them are trimmed close before storage, there isn’t much for them to eat except the roots. I think they actually tried to bury food in the pots, not eat the plants. There is a steady supply of bird seed for them to eat, so I don’t think they are really tempted.
If you find yourself with an embarrassment of riches at the end of the growing season, give yourself permission to hide them under a pile of leaves. The plants in those containers will thank you for it!